The present invention relates to leading edge flap assemblies for airplane wings and more particularly to a seal assembly for sealing the slot between the aft portion of a leading edge flap and the leading edge of a wing when the flap is extended.
Leading edge flaps of the Krueger type and variable camber leading edge flaps such as disclosed in U.S. Pat. No. 3,504,870 to Cole et al. are normally stowed in a recess in the bottom of the wing adjacent the leading edge when they are not in use. When extended, the flaps are swung out of the recess in the wing to a position forwardly of the leading edge of the wing and are oriented so as to increase the camber and chord of the wing for takeoff and landing maneuvers. When extended, the structure of the leading edge flap inherently creates a gap or slot between the aft portion of the flap and the leading edge of the wing. In normal use, the air pressure on the top of the wing is less than it is below the flap and below the wing. This differential pressure causes air to flow from below the flap through the slot to the upper surface of the wing. Depending upon the particular flap design and the wing and trailing edge flap with which the leading edge flap is to be employed, the air flowing through the slot can disrupt the smooth airstream flowing over the top of the wing and cause a reduction in lift. It has therefore been found desirable in some instances to employ a seal, normally affixed to the leading edge flap, that closes this slot to prevent airflow through it.
One type of seal that has been used comprises a long, elongate, resilient member that is affixed to the aft portion of the leading edge flap along its entire span. After the flap is extended or as it is extended, the seal is mechanically motivated toward the leading edge of the wing to engage the leading edge and seal the slot. Although such seals are effective for the intended purpose, they are relatively complex and expensive to manufacture and install on aircraft. Moreover, the mechanical actuating mechanism adds weight to the overall flap assembly, ultimately reducing the payload of the aircraft. In addition, the seals have been difficult to construct so that constant contact between the seal and the leading edge of the wing is maintained. Consequently, some of the mechanical seals have tended to leak, allowing some reduction in lift and thus not completely filling their intended purpose.
Another type of seal that has been employed to close the slot between the leading edge flaps and the wing are the constant contact or friction type. This type of seal is permanently affixed to the aft portion of the underside of the flap. As the flap is extended, the seal contacts the wing and, because it is resilient, compresses or flexes between its flap attachment bracket and the leading edge of the wing. When the seal is in place, it is partially compressed so as to form an effective closure for the slot. This type of seal is simpler than the mechanically actuated type, less expensive and is lighter. However, the problem of non-uniform contact between the seal and the leading edge of the wing remains because this type of seal necessarily has a limited compression distance. Compensating for the non-uniform contact requires completely readjusting the seal location on the flap relative to the wing leading edge. Moreover, the fixed seal must rub on the leading edge of the wing as the flap is extended in order to compress it sufficiently to prevent airflow between the seal and the leading edge of the wing. Through many cycles of retraction and extension of the flap, the constant rubbing between the seal and the leading edge of the wing causes wear on both the seal and the leading edge, requiring periodic replacement of the seal or the leading edge skin or both.
It is therefore a broad object of the present invention to provide a light, inexpensive, simple seal construction for closing the slot between the leading edge flap and the leading edge of the wing. Further objects of the present invention are: to provide a seal assembly that minimizes or eliminates the rubbing contact between the seal and the leading edge surface of the wing during the retraction and extension cycles of the flap; to provide a seal assembly and seal member that will uniformly contact the leading edge of the wing despite slight contour variations in the wing; to provide a seal assembly that is usable with a variety of flap configurations, including fixed camber and variable camber flaps; to provide a seal assembly that allows greater freedom in designing the extended flap position, especially the positioning of the trailing edge of the flap relative to the leading edge of the wing and the angular orientation of the extended flap relative to the chord line of the wing; and to provide a seal assembly that is essentially self-actuating in that no mechanical motivation is necessary.